The lawsuits were filed by women who claim use of Premarin and Prempro caused them to develop breast cancer. At one time, Pfizer face around 10,000 breast cancer lawsuits involving the drugs, including 8,000 cases consolidated in federal court in Arkansas, Bloomberg said. In its most recent regulatory filing, submitted on November 19, Pfizer indicated it has now settled almost 5,000 of the suits.

Pfizer first disclosed the $772 million reserve and in May said it had resolved about 3,300 Prempro and Premarin lawsuits. In this most recent filing, Pfizer said it has $260 million reserved for the remaining Prempro cases. However, the company also acknowledged that the figure was just an estimate of what may be needed to settle the lawsuits, and warned “additional charges may be required,”

One plaintiffs’ attorney agreed, telling Bloomberg that the reserve is “grossly insufficient” considering “the size of the jury verdicts to date, and the fact that multiple appellate courts have now affirmed some of those verdicts.”

Pfizer inherited the Prempro and Premarin lawsuits when it acquired Wyeth in 2009. According to Bloomberg, Pfizer has lost 10 of the 18 lawsuits that have made it to jury trials since 2006, though some of those verdicts were later thrown out or had the awards reduced. Earlier this month, a Philadelphia jury ordered Pfizer units to pay more than $72 million in compensatory damages to two women who alleged Prempro and Premarin caused their breast cancer. The case was settled before the jury had a chance to award punitive damages.

For decades, women took drugs like Prempro and Premarin to cope with the symptoms of menopause. However, in 2002 the Women’s Health Initiative (WHI), a major study conducted by the National Institutes of Health (NIH), determined that Prempro and similar drugs significantly increased the risk of stroke, blood clots, heart attacks and breast cancer. The results were so alarming that the NIH canceled the study, citing risk to the participants. The authors of the study suggested that many of the women who used the medications should quit and talk to their doctors about alternatives.

Those findings prompted a wave of litigation, with thousands of women alleging that doctors and patients were not properly warned that the drug may increase the risk of breast cancer. Some complaints even claimed that Wyeth intentionally hid the risk of breast cancer associated with the medications.